Polyvinyl acetate emulsion containing an alkoxy glycol ether, and a base coated therewith



Patented May 6, 1952 UNITED STATES PATENT POLYVINYL ACETATEEMULSIONCONTAIN- FFICE ING AN ALKOXY GLYCOL ETHER, AND A BASE COATEDTHEREWITH Walter G. Kunze and Raymond Bertram Evans, Catonsvillc, Md.,assignors to Le Pages Inc., Gloucester, Mass a corporation ofMassachusetts No Drawing. Application April 6, 1950, Serial No. 154,422

hesives. ,It is particularly concerned with such panemulsionrof polymerswhich is capable of pro- 2 toluene and peroxides. Inmost instances itwas required that the substances be added to the polymer emulsionimmediately prior to use as the resulting compositions were unstableandviding a water-resistant bond or coating and 5 certain of the substancesresulted in a progreswhich at the same time retains the stability, siveincrease in the viscosity of the emulsion until fluidity and the variousother physical propera gel was formed. Gelling rendered the comties 9Such an emulsion Which make it D position unfit for use in adhesiveapplicator maticularly useful as a coating or adhesive. chines operatedat high speed. Additionally, the

The use of melts and solutions of water in- 10 modification affected bysome of these substances soluble artificial resins in the coating andad- ,hesive art has been supplanted to a large extent by emulsions ofsuch resins, particularly polyvinylacetate emulsions, due to theimproved ease, economy and safety with which aqueous emulsions of theresin may be employed. On the other hand, the usefulness of waterinsoluble polymer emulsions has been limited by the characteristic lackof water-resistance of the coatings and bonds deposited therefrom atroom temperatures and the tendency of such coatings and bonds tore-emulsify or disintegrate when subsequently brought into contact withwater during the course of normal use of the object or article to whichthey have been applied.

This lack of water-resistance has been considered innate in the coatingsand films deposited from such polymer emulsions inasmuch as Watersolubleemulsifying and bodying agents are employed necessarily to establish andstabilize the emulsion. These agents are apparently carried into thefilm or bond deposited from the emulsion upon application of theemulsion to a surface,- and actively exhibit the emulsifying effect onthe polymer comprising the body of the coating or;- film1and cause itsredispersion when the surface is-brought into contact with water.

Various; proposals have been made to obviate the water-sensitivity ofthe coatings or bonds deposited fromsuch emulsions, but ingeneral theseproposals have been d rected to 'rrodifying emulsions of such polymerswhich have been prepared in a specific manner, or require treating theemulsion; with certain diluents immediately prior" to its pplica-tiondue to the recognized tendency oft g e suggested diluents to eitherbreak or-gel-the-emulsion shortly after the addition of the diluent.

Prior to the instant invention, for exam le, a common expedient forincreasing the water-resistance of a coating or film deposited from awater-insoluble polymer emulsion included the addition of-a quantity ofone or more substances such as dimethylol urea, trimethylol melamine.certain chromium salts, strong acids'or highly reactive-aldehydes suchas glyoxal, certain resins,

did not result in a substantial improvement in the water-resistance ofthe coating or film deposited from the emulsion, and often impartedundesirable color and foaming characteristics to the emulsion.

Where thermo-plastic polymeric material has been employed, it has beensuggested that the water-resistance of the coating or bond depositedfrom an emulsion of the material can be improved by heating the coatingor bond suificiently to cause coalescence of the material into ahomogeneous mass. This procedure is obviously not suitable where theemulsion is employed as a quick-setting adhesive in high-speedmechanical applicators, and in any event the drying and heatingsuggested is often impractical.

A further suggestion directed to retaining the advantages of workingwith the polymers in an aqueous medium and at the same time avoiding theinherent disadvantages of water-sensitivity of the coatings or filmsdeposited therefrom requires dispersing the polymer as extremely smallparticles. The coatings or films deposited from such emulsions doexhibit a satisfactory water-resistance, but due'to the fine particlesize which imparts the water-resistance, the emulsions do not have thetack necessary to make them useful as quick-setting adhesives.

It is an object of this invention to provide a com osition comprising anaqueous emulsion of a polymer, particularly a polymer of vinyl acetate,alone or in combination with small quantities of other monomers, whichis stable throughout long periods of storage, andwhich when employed asa coating or as an adhesive will deposit a coating or bond which ishighly water-resistant. A further ohieot of the in ention is to providea process which is generally applicable to modify emulsions of olymers,particularly polyvinyl acetate. which have been polymerized to diiierentextents, or in different manners, and which include various combinationsof plasticizers and other diluents commonly employed to develop favoredcharacteristics in the films or coatings d posited from such emul ions.

Weh-ave discovered that the water-resistance of coatings or bondsdeposited from an aqueous emulsion of polymers, particularly polyvinylacetate emulsions, which are formulated, or modilied, to have atackiness rendering them suitable for use as quick-setting adhesives,can be established by additions of one or more of a certain group oforganic compounds within specific limits. These active compounds arecharacterized by a particular balance between the parts of the monomericmolecule, one part of which is hydrophilic or polar in nature, and theother part of which is hydrophobic or non-polar. The effectiveness ofthe compounds in producing waterresistance in the coatings or bondsdeposited from such emulsions is apparently due to the presence of boththe polar and non-polar groups within the molecule in the prescribedbalance.

As a class, these active compounds exhibit solubility, to variousextents, in both water and in organic solvents such as mineral spirits,petroleum ether, toluene, castor oil, etc. This solubility in both waterand organic solvents apparently is due to the dualhydrophilic-hydrophobic nature of the compound. As it has been generallyrecognized that the presence of Water-soluble emulsifiers carried intothe bonds and coatings deposited from emulsions of water-insolublepolymers may later cause redispersion and disintegration of the bondsand coatings, it was particularly surprising to find that incorporatinginto the emulsion additional compounds which are water-solublethemselves will nullify the effect of the water-soluble emulsifiers andthereby impart water-resistance to the coatings and films deposited fromsuch emulsions.

For present purposes a polar or hydrophilic group or radical may beconsidered to be one which has a strong affinity for water and whichwhen combined in compounds in which it is the dominant functional groupwill cause the resulting compound to be immiscible, or miscible to alimited extent, in oil-type solvents. A non-polar or hydrophobic group,on the other hand, may be considered to be one which has slight affinityfor water and a strong aflinity for oil-type solvents. The hydroxylgroup, for example, has a strong polar character. Certain carbon chains,particularly those having from 4 to 8 carbon atoms may be considered asnon-polar.

The prescribed balance between polar and nonpolar portions of themolecule has been found in etherified glycols which contain from 6-10carbon atoms. Compounds of this group have been found to be effectivewhether partially or totally etherified. For example, both diethyleneglycol monoethyl ether and diethylene glycol diethyl ether are effectivein producing water-resistance in the films and bonds deposited frompolyvinyl acetate emulsions. In the case of the latter compound, thealkoxy groups substituted for the hydroxy groups similarly exhibit polarcharacteristics but to a lesser extent. In th same manner, the glycolsmay be partially etherified, and partially 'esterified by thesubstitution of the polar acetate group for one of the hydroxy groups.The resulting compound is active as long as the required polar-non-polarbalance is retained by limiting the carbon atoms present in th moleculeto 6 to 10. Examples of these latter type of active compounds areethylene glycol monoethyl ether acetate and diethylene glycol monoethylether acetate.

The criticality of the prescribed polar-nonpolar balance in themolecules of the active compounds is evident from the fact that ethyleneglycol, having a two carbon atom chain and two hydroxyl groups, wasfound to be too hydrophilic to effect water-proofness, but when modifiedto ethylene glycol monobutyl ether, wherein 6 carbon atoms were presentin the molecule with one hydroxyl group, the compound was effective.Diethylene glycol, ethylene glycol monoethyl ether, and diethyleneglycol monomethyl ether, having respectively 4, 4 and 5 carbon atomsalong with one hydroxyl group are not effective. On the other hand,carbitol, having 6 carbon atoms and one hydroxyl group is effective.

Other outstanding active compounds of this type are diethylene glycolmonobutyl ether, 2- methoxy methyl, 2, 4, dimethyl pentanediol, l, 5 and2-ethoxy methyl, 2, 4 dimethyl pentanediol, 1, 5. If the number and/ orstrength of the polar groups is increased beyond the specified relationship to the non-polar residue of the molecule the compound becomes toohydrophilic and will not produce water-resistance. Conversely, if thenon-polar portion of the compound becomes dominant the compound becomestoo hydrophobic and either no water-resistance results or the coating orfilm formed therefrom becomes rubbery and has no bond strength afterwetting-out. In addition to achieving the necessary balance between thepolar and non-polar portions of the molecule of the active compounds, itis also necessary to add the compound to the polyvinyl acetate emulsionin certain limited proportions, which vary to some extent according tothe initial characteristics of the starting material emulsion, theemulsifiers employed in formulating the starting material emulsion, theaverage size of the dispersoid, the amount of plasticizers or otherdiluents present in the starting material emulsion, the age of thestarting material emulsion, and the rate at which the composition isformulated, as will be apparent from the following description andexamples.

The preferred range of quantities of one or more of the active compoundsby weight with respect to the solid content of the polyvinyl acetateemulsion has been found to be between about 1-25%.

The physical properties of a polyvinyl acetate emulsion such as theviscosity of the emulsion and the tensile strength, flexibility and heatsealing temperature of the film or bond deposited from the emulsion aredetermined in a large part by the degree of polymerization of the vinylacetate monomer. A higher degree of polymerization results in increasedbond strength, a higher heat sealing temperature and a somewhat higherinitial water-resistance, which is, however, considerably less thanrequired commercially for a water-resistant coating or bond. A lesserquantity of the active compounds is necessary to impart the desiredwater-resistance to the deposited coatings or bonds when the relativelygreater water-resistant emulsions are employed as a starting material.The age of the starting material emulsion also determines thesusceptibility of the emulsion to Water-proofing, the older emulsions,for example, emulsions several months old, show better water-resistancethan those freshly made.

For present purposes the polyvinyl acetate starting material emulsionshaving sufficient tack to be useful as quick-setting adhesives andsuitable for improvement according to the instant invention may beclassified according to their initial water-resistance although in eachinstance the water-resistance is negligible from the stancnointsof miimumrcommemiai re uirets. uch:- emu s-ions en ra l co tai -,1 abouLEO-60% polyvinylacetate by weight and a bond produced, by therespective emulsions between "twosheets of mildly calenderedwhite-sulphite paper-twill open up within 23 hours after immersion inwater atabout 25 C.

:Such emulsions which include the commercial- ;ly available emulsionsknown asElvacet No. 80- "900, Elvacet 81-4300, Gelva 3-50, Polyco 117B,Polyco '289 and 'Polyco 117SS produce bonds which show practically nowater-resistance on immersion.

Although the most important aspect of the -instant inventionv concernsestablishing waterresistance ofbonds'deposited from polyvinylacetate-emulsions which showno initial water-resistance; it will-beapparent that thesame compounds which improve the emulsions showing noinitial water-resistance will be equally effec tive in lesser quantitiesin emulsions which deposit bonds which show someinitial water-re--.-sistance.

as aresult of particular plasticizers employed.

In general, however, the variations which tend to increase the relativeinitial water-resistance of the starting material emulsions lessen thequantity of the active compoundsrequired to efiect completewater-resistance. I

The amounts of active compound required to produce maximumwater-resistance in a particular emulsion also varies with the quantityand the nature of the plasticizers, extenders, or other diluents whichmay be used to develop desired characteristics of fluidity or tackinessin the emulsion, or of flexibility, hardness, etc, in the coating orfilm deposited from the emulsion. In general, it has been found. thatthe insoluble type of plasticizers and resins in commonuse increase theeffectiveness of the active compounds, and that a lesser quantity ofactive compound is necessary to produce complete waterresistance whensuch plasticizers are also present in the emulsion. It should be noted,however, that in each instance the emulsion containing the plasticizersand various other diluents was not initially water-resistant and thatthe addition of the activecomoound is necessary to aifect anysatisfactory water resistance, although as related above. a lesseramountis necessary when insoluble plasticizers are also present.

This enhancing effect of the insoluble plasticizers was particularlyobserved with respect to dimethyl phthalate, dibutyl phthalate,chlorinated diphenyls, methyl abiatate and tributyl phosphataandappearstobe characteristic of,

other common plasticizers such as di-carbitol I phthalate,dibutoxy-glycol phthalate, dimethoxyglycol ,phthalatabutyl phthalylbutyl. glycolate, methyl phthalyl ethyl glycolate, triglycol di-2-ethylbutyrate, triglycol di-Z-ethylhexoate, tricresyl phosphate andtriphenyl phosphate.

.On the otherhand, the presence of I a small amount ofcertainwater-soluble thickeners such as polyvinyl alcohol and sodiumcarboxymethyl v cellulose tend to increasethe. amountof active perminute.

FQII EQH l .n sSaJ- t e f maximum-w t resistance.

In someinstances care must be;exercise d to avoid breaking the emulsionby sudden heating, or by extended heating above the temperaturespecified. The critical temperature will vary, of course, with thecharacter of the particular starting material emulsion employed.

acetate emulsion without materially interfering with the versatility ofthe starting material emulsion. It will be noted, however, that any ofthe active compounds having therequisite polar-non-polar balances in themolecules thereof are effective in producing water-resistance when usedin quantities within the range of 4-25% by weight of the solids presentin the starting material polyvinyl acetate emulsion. The minimum amountof a particular one of the active compounds depends upon the variousfactors previously discussed, but in all instances is within the rangereferred to above. Compositions having up to 50% by weight of activecompound with respect to the solid content of the polyvinyl acetatestarting emulsions may be employed, especially where the active compoundhas plasticizing properties which are desirable and the cost of thecompound is not prohibitive. In most instances, however, the maximumwaterresistance is obtained with the least effect on other physicalcharacteristics of the composition when a total of from 715% of activecompound or compounds by weight of solids in the starting materialemulsion are employed. This latter range is particularly suitable whenemploying diethylene glycol monobutyl ether as the active compound. Someof the numerous possibilities which exist in formulating a waterresistant composition within the operable limitations specified aboveare illustrated in the following examples.

The addition of the active compound to the starting material emulsionmay result in a substantial increase in the viscosity of the emulsion toform a cohesive mass unless the active compound is added slowly withcontinuous agitation. In some instances rapid addition of the activecompound results in localized precipitation of the emulsion. The largestpart of the increased cohesiveness and viscosity of the emulsion causedby addition of the active compound at a suitable rate disappears onagitation, or when the treated emulsion is permitted to stand for ashortperiod following the addition of the active compound. The waterproofproperties ,of the compositions can be improved by the.addition of waterto the mixture of the starting material emulsion and the active compoundin quantities necessary to bring the solid content down to between40-50% by weight.

In all of the following examples the composition was prepared bystirring the starting material'emulsion with a Lightning Mixercontinuously during the addition of the active compound thereto. Theactive compound was introduced into the emulsion at the rate of about 3%of the total weight of the active compound The preparation ofthe-composition may be done at normal ambient temperatures.

Each of the tacky starting material polyvinyl emulsions was applied as acoating on the surface of a moderately calendered and sized Whitesulphite paper and as a bond betweentwo such papers. The films and bondsthus formed were allowed to dry for 24 hours at room temperature andwere thereafter immersed in water at room temperature for 24 hours. Uponremoval from the water the wet strength of the paper exceeded the bondstrength in all cases, and the bond ruptured when the bonded papers wereseparated. The coatings in each instance had visibly disintegrated.These starting material emulsions were, therefore, considerednon-water-resistant, and in the subsequent experiments, satisfactorywater-resistance of a film or bond formed from -an emulsion treated withan active compound Easample 1 110 parts of a tacky polyvinyl acetateemulsion having a solid content of about 58% were introduced into amixing vessel and stirred continuously with a Lightning Mixer as 3 partsof a dimethyl phthalate plasticizer were added. To this mixture 2 /2%diethylene glycol monobutyl ether by weight of the solids of thestarting material emulsion was added slowly while the agitation wascontinued. Similar samples were prepared using respectively l, 10, 12and 50% diethylene glycol monobutyl ether by weight of the solid contentof the starting material emulsion. Each of the samples thus preparedwere applied as both a film and bond to a moderately sized andcalendered white sulphite paper. After the films and bonds werepermitted to dry for 24 hours they were immersed in water at roomtemperature for an additional 24 hours. At the end of this period it wasfound that all samples which contained 4% or more of diethylene glycolmonobutyl ether had deposited waterproof films and bonds. In theseinstances the bond strength exceeded the wet strength of the paper afterthe 24 hour immersion.

Example 2 '7 sample compositions were prepared by mixing 220 parts of apolyvinyl acetate emulsion having about 55% solid content with 12 partsof a methyl abiatate plasticizer and respectively 2 A;%, 4%, 5%, 7 10%,and by weight of the solid content of the starting material emulsion ofdiethylene glycol diethyl ether. The diethylene glycol diethyl ether wasadded slowly while the mixture of plasticizer and starting materialemulsion was continuously agitated. Thereafter, all the samples werediluted with water to reduce the polyvinyl acetate solid content tobetween -45%. Each of the samples was then applied to a moderately sizedand calendered white sulwhite paper as both a film and bond. After thefilms and bonds were permitted to dry for 24 hours they were immersed inwater at room temperature for 24 hours. At the end of this time all ofthe samples containing 4% and more of diethylene glycol diethyl etherwere found to have deposited waterproof films and bonds.

Example 3 To 220 parts of a tacky polyvinyl acetate emulsion havingabout 55% solid content were added 5% of dimethyl phthalate plasticizerand 5% of dibutyl phthalate plasticizer by weight of the solid contentof the starting material emulsion. This mixture was agitated and 12%ethylene glycol monobutyl ether by weight of the solid content of thestarting material emulsion was added thereto. Other samples wereprepared by adding 14% and 20% ethylene glycol monobutyl ether by weightof the solid content of the starting material emulsion. All 3 sampleswere tested for waterproofness in the manner described in the precedingexamples and were found to deposit waterproof films and bonds.

Example 4 To 220 parts of a tacky polyvinyl acetate emulsion havingabout 55% solids were added 25% diethylene glycol monoethyl ether byweight of the solid content of the emulsion. The addition of the glycolwas made slowly while the emulsion was constantly agitated. Thereafter,the emulsion was diluted with water to reduce the solid contents thereofto about 45%. The resulting composition was tested for waterproofness asdescribed in Examples 1 and 2 above and the films and bonds depositedtherefrom were found to be waterproof.

Example 5 To parts of a tacky polyvinyl acetate emulsion having about55% solid content were added 20% by weight of the solid content of theemulsion of diethylene glycol monoethyl ether acetate. A second samplewas prepared by adding to the same amount of starting material emulsion20% by weight of solid content of the emulsion of ethylene glycolmonoethyl ether acetate. The addition in each instance was made whilethe starting material emulsion was being agitated. Each sample wasapplied to a moderately sized and calendered white sulphite paper asboth a film and bond. The films and bonds were tested for waterproofnessin the manner described in Examples 1 and 2. In each instance the filmand bond were waterproof.

It will be apparent that the water-resistant compositions formulatedaccording to the instant invention will considerably extend theusefulnes of aqueous emulsions of polyvinyl acetate into the field inwhich high water-resistance of the bond or coating deposited isnecessary, and will find application in bonding or cementing forcellulosic articles such as paper cups which in the course of normal useare exposed to water, and for bonding surfaces of cellulosic material toother surfaces of a hydrophilic character such as masonry. These instantcompositions are particularly adapted for use as a sizing wherewater-resistance of the fabric or the paper to which it is applied isrequired. It may also be employed in the composition of printing paste,as a. finish for paper, paper-board, or foils and in the manufacture offormed or impregnated goods, as well as in distemper paints and thelike.

Having thus described the invention, what is new and desired to besecured by Letters Patent 1s:

1. A composition comprising a tacky emulsion of polyvinyl acetate havingfrom 40-60% by weight of solid contents, and from 4-50% by weight ofsaid solid content of 'diethylene glycol monobutyl ether.

2. A composition comprising a tacky aqueous emulsion of polyvinylacetate having 40-60% by weight of solid contents, a plasticizer forsaid acetate, and from 4-50% by weight of said solid contents ofdiethylene glycol monobutyl ether.

3. A composition comprising polyvinyl acetate, and from 4-50% by weightof said acetate of diethylene glycol monobutyl ether.

4. A composition comprising a tacky emulsion of polyvinyl acetate havingfrom 40-60% by weight of solid contents, and from 4-50% by weight ofsaid solid content of diethylene glycol monoethyl ether.

5. A composition comprising a tacky emulsion of polyvinyl acetate havingfrom 40-60% by weight of solid contents, and from 4-50% by weight ofsaid solid content of diethylene glycol diethyl ether.

6. A composition comprising a tacky emulsion of polyvinyl acetate havingfrom 40-60% by weight of solid contents, and from 4-50% by weight ofsaid solid content of ethylene glycol monobutyl ether.

7. A composition comprising a tacky emulsion of polyvinyl acetate havingfrom 40-60% by weight of solid contents, and from 4-50% by weight ofsaid solid content of 2 methoxy methyl, 2,4, -dimethyl pentanediol, l,5.

8. A composition comprising a tacky aqueous emulsion of polyvinylacetate and from 4-50% by weight of said acetate of an etherified glycolcontaining not more than two glycol residues having not more than 6carbon atoms and at least one alkyloxy group having 2 to 6 carbon atoms,said etherified glycol having a total of 6 to 10 carbon atoms.

9. A composition comprising a tacky aqueous emulsion of polyvinylacetate, a plasticizer for said acetate, and from 4-50% by weight ofsaid acetate of an etherified glycol containing not more than two glycolresidues having not more than 6 carbon atoms and at least one alkyloxygroup having 2 to 6 carbon atoms, said etherified glycol having a totalof 6 to 10 carbon atoms.

10. A process for formulating a water-resistant adhesive which comprisesthe steps of adding to a tacky polyvinyl acetate emulsion having a solidcontent of from 50-60%, an etherified glycol containing not more than 2glycol residues having not more than 6 carbon atoms and at least onealkyloxy group having 2 to 6 carbon atoms, said etherified glycol havinga total of 6 to 10 carbon atoms, and thereafter diluting the saidemulsion with water to reduce the solid content thereof to -45%.

., WALTER G. KUNZE.

RAYMOND BERTRAM EVANS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Collins et al June 29, 1948 Number

1. A COMPOSITION COMPRISING A TACKY EMULSION OF POLYVINYL ACETATE HAVINGFROM 40-60% BY WEIGHT OF SOLID CONTENTS, AND FROM 4-50% BY WEIGHT OFSAID SOLID CONTENT OF DIETHYLENE GLYCOL MONOBUTYL ETHER.